The invention relates to a cathode ray tube comprising an electron gun, in which an electrically insulating surface is covered with an electrically insulating film.
Such a cathode ray tube is known from U.S. Pat. No. 4,473,774.
In operation, one or more electron beams are generated in cathode ray tubes. Cathode ray tubes are used in, inter alia, television receivers, electron microscopes, oscilloscopes, X-ray detectors, image intensifiers, photomultipliers, ion-implantation apparatuses and other devices. Within the framework of the invention the term electron gun is to be understood to mean a means of generating electrons. The electrons may be generated in the form of an electron beam.
A problem which occurs in cathode ray tubes is that, in operation, surfaces inside the cathode ray tube are charged. Such charging phenomena occur, in particular, on electrically insulating surfaces. As a result thereof, negative effects may occur. For example, flashover between components of the cathode ray tube ("arcing") and undesirable light effects ("blue glow") may occur. These effects are also referred to herein as the high-voltage behaviour of the cathode ray tube. U.S. Pat. No. 4,473,774 discloses a cathode ray tube having an electron gun arranged in the neck. The inner side of the neck is covered with a film of a non-ionic organic copolymer. The cathode ray tube disclosed in U.S. Pat. No. 4,473,774 should comply with the following requirements:
1. The copolymer used does not degrade at the temperatures which are customary during the manufacture of a cathode ray tube, i.e. the film should inter alia be heat resistant. PA0 2. Steps must be taken to prevent the film from becoming detached. PA0 3. The applied film cannot withstand RF spot-knocking (RFSK), which is a frequently used method in the manufacture of cathode ray tubes. PA0 4. Care must be taken that the film does not become overheated during manufacture of the cathode ray tube.
As a result of the above-mentioned drawbacks the cathode ray tube as described in U.S. Pat. No. 4,473,774 is not suited for mass production. Only very few materials are suitable and the manufacturing method should comply with very stringent requirements.